This invention relates to a weighing system that can be permanently or temporarily attached to an object such as a bed, chair, chaise lounge, sofa or the like. The weighing system has improved accuracy by reducing non-centered and side directed force components and may be used to determine the weight of patients in a plurality of types of hospital beds, chairs, or for home use.
It is frequently desirable to accurately monitor the weight of a patient confined to a bed, chair, etc., whether in a hospital, at home, or in other treatment settings, and to observe changes in weight to monitor the health of the patient and ensure that proper dosages of medication are administered. It is difficult, however, to weigh seriously ill patients or persons with limited mobility by removing them from the bed on a regular basis. Critically ill patients, in particular, may require frequent weighing, with their severe physical condition preventing their removal from bed.
Beds incorporating weighing systems, such that the patient need not be removed from the bed to be weighed, have been disclosed, for example, in Reichow et al., U.S. Pat. No. 5,269,388, Geringer U.S. Pat. No. 5,823,278 and Carruth et al., U.S. Pat. No. 4,926,951. The system disclosed in Reichow et al. utilizes load cells which are rigidly mounted along the sides of the bed frame. The Carruth system utilizes a separate weigh frame mounted to the bed frame. These systems are generally an integral part of the bed, and must be incorporated into the bed when it is manufactured. Beds incorporating these weighing systems are generally more expensive than ordinary beds without a weighing system, are typically permanently attached, and are also heavier, making it more difficult to move such beds. Geringer similarly requires the use of a set of four load cells, one secured upon each bed leg in which the weight of the patient must be determined. The secure attachment described in Geringer makes no provision for minimizing off center or non-vertical, side directed forces which interfere with the accuracy of the load cell weight determination. In Geringer, the caster mounted weighing system may also be used to address a number of other types of weighing applications, in addition to bed weighing systems.
It is, therefore, an object of this invention to provide a relatively inexpensive, accurate portable weighing system which may be used with any of a plurality of beds, chairs, platforms, etc. in a hospital, nursing home, residence or other care facility in which the weigh system is not permanently installed on one of the beds, but may be used to establish the weight of the occupant of any bed or other support structure selected.
It is also an object of this invention to provide a relatively inexpensive, accurate weighing system which may be removably and temporarily installed on a various objects for the purpose of weighing the object or its contents which minimize or eliminate off center or non-vertical force components which interfere with the accuracy of the load cell weight determination.
In scales generally, it is conventional to mount a weigh frame above a base and rigidly connect load cells between the weigh frame and the base. A subject to be weighed is placed on the weigh frame, the stressing of the load cells, through the application of the weight, causes the load cells to generate an electrical signal proportional to the weight applied to the load cells. The loads measured by respective load cells are summed to provide the measure of the weight of the subject on the scale.
The rigid or substantially rigid connection between the base and the weigh frame is usually satisfactory where the base is fixed with respect to ground. But where the scale is to be moved from place to place on a regular basis, or where the load is applied in diverse directions or attitudes, thereby introducing force vectors that are not parallel to the force of gravity, the rigid mounting of the weigh frame with respect to the base frame will introduce errors. Any twist of the weigh frame with respect to the base frame will cause binding at the load cell. The frictional force of the binding will be seen as weight that is either added to or subtracted from the true weight, but in any event, will introduce error.
A hospital bed having provision for weighing a patient is an example of the type of weight determination environment that causes error. This is particularly true in relation to special critical care-type beds that are leased for limited periods, returned, and leased again for use at another site. The frequent movement of the bed from one site to another compounds the problems referred to above for permanently mounted weighing mechanisms. A ground support that is not precisely perpendicular to the force of gravity may introduce a twist of the bed frame causing error. Similarly, non-vertical off center or side directed force components may introduce error in the securely and rigidly coupled weighing systems of the prior art. The position of the patient may change the vector of the load on the load cell. Any change from a strictly vertical application of the load, that is, parallel to the force of gravity, may introduce unwanted and unacceptable error in the weights being determined.
Additionally, it is undesirable to have the weigh system for hospital beds permanently attached to the bed, since it is necessary in such systems to have a complete system for each bed. In facilities having many beds, the cost of separate weigh facilities for each bed is substantial. Particularly in nursing home and extended care facilities it is frequently not necessary to check a patient""s weight every day, and having a portable system which may easily be used on various beds in the care facility at various times would be a substantial cost savings. In many installations, a single set of weighing devices may suffice for the entire facility.
It is an objective of the present invention to provide a load c(ell weighing system, particularly useful in the accurate and reproducible measurement of weight of the occupant of hospital or nursing home beds, that may be conveniently and removably attached to and used with a plurality of such beds. Weighing error is held to a minimum notwithstanding the surface on which the bed is mounted or the deviation from horizontal of the attitude of the patient on the bed by the use of individual weight measuring load cells individually attachable and removable from each leg of a hospital bed. The electronic output of the four load cells is conducted into a central computing station where the total weight measured by the four load cells is determined. The information from each of the individual load cells may conveniently be conducted to the bedside monitor or to a central nurse""s station for review and recording.
The objective of the present invention is attained by removably connecting four load cells, one upon each leg or frame engaging support of the hospital bed. Each load cell is connected to its respective leg or frame support and the mechanism activated to transmit the weight carried by the respective leg or support through a load cell. The weight measuring load cell structure is configured so that the weight carried by a leg of the bed is transmitted vertically downwardly through the load cell to provide an accurate weight readout for that leg. The sum of the four load cells indicates the total weight of the bed and its occupant. The tare weight of the bed without the occupant can readily be measured while the occupant is absent and the patient""s true weight determined by subtracting the tare weight from the total weight. The subtraction may be done conveniently and automatically by the push of a button at the bedside panel or at the nurse""s station.
A preferred embodiment of this invention includes a cup adapted to receive the bed leg or support while permitting limited vertical movement therebetween. The load cell is positioned directly below and attached to the cup with a multipurpose fastener, again with limited vertical movement permitted between the cup and the load cell. The arrangement is such that the bed leg or support may move downwardly into contact with the exposed head of the multipurpose fastener without having the cup engage the load cell upper surface. In this manner vertical weight components are directed vertically into the load cell and extraneous off-center and side directed loads avoided. An alternative structure utilizes the curvature of a castor wheel engaging the upper surface of the load cell so that only vertically-directed weight components are imposed upon the load cell. An embossment or bushing may be interposed between the load cell and the cup to issue insure that weight forces are properly transmitted into the load cell.
When the embodiment of this invention utilizing the castor wheel is used, a bed jacking mechanism may be used separately from the load cell to raise the bed to a sufficient height, usually no more than 3 to 4 inches, to permit easy insertion of the castor wheel into a retainer on the top of the load cell. Using this approach, the bed needs to be raised only a small distance in order to transfer the weight carried by the bed leg through the castor into the load cell and thereby determine the weight carried by that leg.
The weighing system of this invention advantageously includes a plurality of removably attachable weight measuring supports which may either be attached to the legs of a bed or can be designed to be placed under the frame of the bed with the legs off the support surface. The supports each have a load cell which has a horizontally disposed floor engaging base, an upper surface, a weight measuring device and a first fastener receiving aperture opening out of said upper surface. A frame engaging bed support is slidably inserted into a bed support engaging cup which has an enclosed side wall and a bottom wall. The cup has a hole or aperture through its bottom wall and a bed support fastener receiving slot in its side wall. A load cell fastener is inserted through the second fastener receiving aperture into the aperture in the load cell, which is preferably threaded, thereby coupling the load cell to the cup through its bottom wall. The fastener has a head of a diameter exceeding the fasten(r receiving aperture so that it will not pass through. The head of the fastener is exposed for engagement by the bottom weight supporting surface of the bed support. The bed support fastener is inserted into the bed support fastener slot and threaded into said bed support to permit limited vertical movement between the cup and the leg. A weight data collector such as a small computer or the like is attached to the load cell output signals to collect and display weight measurement generated by the load cells so that when the bed is supported upon the weight measuring supports, the cup does not engage the load cell and as a result, predominantly vertically directed forces are transmitted to the load cell with side directed or off center forces minimized.